Local media reports say tens of thousands of Argentine fans remain in the country. They appear to be overwhelmingly young and male: Most are in their 20s, and less than a third of them are women.
Brazil's Federal Police did not respond to email and telephone requests seeking confirmation of how many Argentines are still here. But the prospect of a large number of foreigners selling handicrafts, juggling at intersections for handouts or relying on government social services for poor Brazilians has officials worried.
Although Brazil's once-gangbuster economy has slowed in recent years, the situation is far better than that in crisis-wracked Argentina, which has a shortage of dollars and one of the world's highest inflation rates.
Antonio Pedro Figueira de Mello, who heads Rio's tourism promotion agency, has acknowledged that controls along Brazil's 780-mile land border with its southern neighbor may have been too lax during the tournament.
"We were taken by surprise" by the influx of Argentines, the Rio newspaper O Globo quoted Mello as saying. "In any place in the world, people have to state where they're going, how much time they're staying, what resources they have and whether they have health insurance. That was not done."
Argentines don't need a visa, or even a passport, to visit Brazil. A government ID card will do.
Mello spoke at the Sambadrome, which was turned into a makeshift campsite to help accommodate the waves of Argentines who arrived by car, bus and motorhome during the World Cup. The site was closed last week, and the last campers were evicted. Media reports said Argentine consular officials were there to help organize return transportation for people whose money ran out or whose documents were lost or stolen, but many reportedly weren't interested in such help.
The stragglers dress mostly in raggedy shorts, T-shirts and flip-flops, bathing infrequently at public water fountains or outdoor showers at the beach. There is no need for warm clothes in Rio, where the temperatures currently hover in the low 80s.
Brazil and Argentina harbor a deep rivalry over soccer, and scattered fights between young men from both nations were seen in Rio and other cities during the Cup. But the lingering presence of the Argentines hasn't seemed to ruffle any feathers.
In fact, Fatima Souza de Oliveira, a 60-year-old high school Portuguese teacher, said she saw the stragglers as an homage to the Brazilian way of life.
"I think it's our relaxed attitude, our beaches and the warmth of the climate and the people that enchanted them," she said. "Everyone who came for the Cup loved it, and they all probably wanted to stay."
The Argentines are not the only World Cup fans intent on remaining in Brazil. Last week, police in the southern state of Rio Grande do Sul said several hundred fans from the West African nation of Ghana applied for asylum after coming in on tourist visas to follow their national team. Brazil is studying the applications.
It could prove much more difficult to control the Argentines, without any visa requirements.
Following their eviction from the Sambadrome, Pontoni and 10 or so of his compatriots moved to a nearby park, where they lounged on the grass with their oversized backpacks. They knotted friendship bracelets and prepared other handicrafts to hawk on the beach.
"I don't think I'm going back," said 25-year-old Martin Sichero, a friend of Pontoni. "I came for the World Cup, but now I think I'm here for good."